灰铸铁中常见的冶金缺陷

1、Common Metallurgical Defects in Grey Cast Irons灰铸铁中常见的冶金缺陷Causes and Cures原因及对策C.M.EcobCustomer Services Manager, Elkem AS, Foundry Products Division艾肯铸造产品部客户服务经理C.HartungResearch Manager,Elkem AS, Foundry Products Division艾肯铸造产品部研发经理S-O.OlsenTechnical Service Manager, Elkem Bjolvefossen AS艾肯技术服务经理A

2、bstract摘要Whilst most foundries today recognise the types of defect found in grey cast irons, an appreciation of the causes and therefore cures is not always apparent.有时候很多铸造能够分辨出灰铸铁中的冶金缺陷，但相应的产生原因和对策却不是很清楚。This paper will examine some of the common metallurgical defects, which have been found during

3、 examination of rejected castings in Elkem's Research Centre in Norway.位于挪威的艾肯研究中心在检查报废的铸件时发现了一些铸造缺陷，本文将认真讨论和研究这些缺陷。Gas defects are particularly difficult to categorise and particular attention is paid to hydrogen,nitrogen and carbon monoxide gas holes.气孔类的铸造缺陷是最难分类的，主要的关注应该集中在氢气孔、氮气孔、和一氧化碳气孔。Ot

4、her defect types examined include shrinkage, flake compaction, Widmanstatten graphite and the commonly seen ferritic rim.其它要讨论的缺陷包括收缩、短片状石墨、和常见的铁素体边缘。Introduction引言Metallurgical defects, whilst normally a small part of a foundry's defect casting percentage, can be time consuming and expensive to

5、 classify and hence remedy. In this paper, some of the more common defects are described based on case studies from Elkem's Research Centre. In the examination of any defect, good metallographic facilities are necessary to provide sufficient detail to avoid mistakes in the correct identification

6、 of the defect, particularly when gas is suspected as the problem. Other defects, such as Widmanstatten graphite, may require high magnifications to be able to see the problem.虽然冶金缺陷只占多铸造厂产品缺陷的很小一部分，但要分析其原因和采取正确的措施却是及其费时和昂贵的。在本文中将根据艾肯研发中心的案例研究来描述一些最普通的冶金缺陷。在任何缺陷的检查过程中，必须拥有良好的设备以便为正确的分析缺陷形成原因提供足够的信息来

7、避免错误，特别是当认为是主要原因的时候。其它的缺陷，像魏氏体石墨，就需要高放大倍数的显微镜。Hydrogen Pinholes氢引起的针孔These may be considered to be one of the most expensive defects as they are not normally revealed until after machining. They can be found both in grey and ductile irons and tend to appear as small spherical holes just beneath the

8、casting surface. The inner surface of the hole will have a continuous graphite lining and hence appear to be black and shiny on examination. This precipitation of graphite onto the surface results in a graphite depleted area around the hydrogen gas hole as shown in Figure 1.氢气孔可能是代价最为高昂的一种缺陷，因为一般它们在

9、机加工后才显露出来，在灰铁和球铁中都会出现，常以圆球状出现在铸件表皮之下。由于气孔的内壁被石墨所覆盖，因此检查的时候气孔内壁是黑色和发亮的。这种气孔内壁石墨的析出导致了气孔外壁产生了石墨的耗尽的区域，这些图片显示在图1当中。Hydrogen pinholes can be caused by several factors, either alone or in combination. Most commonly, high levels of aluminum or titanium in the base iron causes a reaction with moisture from

10、 the greensand, damp tools or wet refractories. Other sources of moisture could be damp or oily charge materials (including rust), a build up of dead clay in the sand system which will tend to retain moisture or the use of old cores, which have picked up moisture from humid atmospheres.有几种因素能够引起单个的氢

11、或成片的氢气针孔，最主要的原因就是铁液中的Al或钛与来自型砂、潮湿的工具，或潮湿的耐火材料中的水汽发生反应。水汽的其它来源可能是湿的空气或者被有污染的炉料、铁锈，型砂中积聚的死粘土也会使型砂的水分升高、也可能使用旧的芯子，因为这些芯子会从潮湿的大气中吸收水分。8 J& 'Example of hydrogen porosity revealed Close-up of hydrogen pinhole revealing inner on machining graphite lining;机加工暴露出的氢气孔 显示了具有内壁石墨膜的特写氢气孔 Figure 1. Hydrog

12、en pinhole.图1 氢气针孔Pinholes may be prevented, or the occurrence reduced, by restricting the aluminium content of the base metal below 200ppm and minimising the titanium content. Careful control of steel scrap, avoidance of CG iron returns (if made using Ti) and elimination of enamelled scrap will hel

13、p in this respect. Some pig irons can also contain titanium.通过将铁液中Al的含量限制在200ppm以下和最大程度的减小Ti含量和防止氢气孔的出现和减少其发生的几率。对废钢的仔细控制、避免使用蠕墨铸铁的回炉料（如果用Ti生产）和去除带釉的废钢有助于减少氢气孔的产生。一些生铁也含有较多的Ti。Care should be taken to fully dry refractory patches and coated tools before use and sufficient new sand added to the mouldi

14、ng system to prevent build up of dead clay. Moisture in the system should preferably be below 3%. Cores and water-based coatings should be fully cured and dry before the metal is poured into the mould.应该采取措施来使所用的耐火泥和涂工刷涂料具干燥，并向砂处理系统中加入足够的新砂来阻止死粘土在型砂中的累积。型砂中的水分最好低于3%，在浇注之前，芯子和涂料必须完全干燥和熟化。Increasing m

15、etal pouring temperatures and carbon equivalents have also been noted to reduce the incidence of this particular defect.现在已经注意到提高浇注温度和提高碳当量能够减少这种特殊缺陷的发生几率。Nitrogen Blowholes氮气孔Example of Nitrogen porosity defect in Close-up of defect showing flake depleted rim grey iron revealed on machining灰铸铁经过机加工

16、后出现的氮气孔 氮气孔周围石墨耗尽区域的特写Figure 2. Nitrogen Blowholes 图2：氮气孔Nitrogen blowholes may be either a surface defect or a sub-surface occurrence. The example shown in figure 2 was only revealed on machining, thus being detected at the most expensive post-foundry finishing operation. Blowholes appear more freq

17、uently in medium to heavy section thicknesses and are often adjacent to resin bonded core or mould materials. The holes, or fissures, are normally irregular in shape (as opposed to the more spherical hydrogen holes) and are perpendicular to the casting surface, protruding some millimetres into the c

18、asting. The inner surface of the hole has a continuous or dis-continuous graphite lining coupled with the subsequent decarburisation in the immediate surrounding matrix. This is clearly seen in figure 2. Also seen in this figure are dendrites, which have grown into the hole. On occasions, the graphi

19、te flakes are seen to have become shorter and thicker, this being a typical sign of high nitrogen.氮气孔缺陷可能在铸件表面或皮下出现，图2是经过昂贵的机加工后处理后在铸件皮下发现的氮气孔，氮气孔更容易在中等壁厚的铸件和靠近使用树脂粘结剂的芯子和造型材料。氮气孔和裂隙状氮气孔一般形状不规则（与圆的氢气孔相比较），垂直于铸件表面，可深入铸件表面以下几个mm。氮气孔内部都有连续的或者不连续的石墨析出膜，与这种析出膜相连的就是周围已经脱碳的基体组织，图2清楚的显示了这一情况，这这幅图片中还能看到伸进氮气孔

20、壁内部的树枝状凸起。有时石墨会变得短而厚，这是氮含量高的典型信号。Nitrogen fissures are caused simply by excess nitrogen in the system. In cupola melted grey irons, this comes from high proportions of steel scrap in the charge which require high levels of coke, whereas in induction melting, poor quality, high nitrogen containing ca

21、rburiser is normally the cause. The use of some resins in the production of cores or moulds can also lead to nitrogen pick up locally within the casting, particularly at a potential hot spot.系统中氮含量高是造成裂隙状氮气孔的主要原因，在冲天炉熔炼铸铁中，高的氮含量来自于炉料中高比例的废钢，熔化这些废钢需要较多的焦炭；在电炉熔炼当中，则是使用了质量差的氮含量高的增碳剂；在制芯和造型中使用树脂粘结剂也可能导致

22、但在铸件的局部累积，特别是在潜在的热节处。Restricting the dissolved nitrogen content to 80 ppm in medium to heavy sections and 120ppm in thin, uncored sections will normally not give nitrogen blowhole problems. In addition, careful selection of raw materials will also help reduce the potential for blowhole problems. Tit

23、anium and zirconium are known to neutralise the effects of nitrogen by producing carbo-nitrides, however care should be taken when using titanium as this can then promote hydrogen pinholes in the presence of aluminium and moisture as previously discussed. Increases in pouring temperature and carbon

24、equivalent are also known to reduce the incidence of nitrogen defects.一般情况下应把薄壁铸件中N的含量限制在120ppm以内，中厚壁的含量限制在80ppm以内，在没有芯子的铸件截面附近一般不会出现N气孔，此外，对认真的选择原材料也能减少N气孔的出现。Ti和Zr能够中和N的有害作用，但是使用Ti是要小心，因为如前面讨论的那样，在较高的Al含量和水的含量下，Ti的存在易使铸件产生氢气孔。提高浇注温度和增加碳当量有助于减少氮气孔缺陷的发生几率。Often, it is very difficult to distinguish b

25、etween hydrogen and nitrogen gas defects. Analysis of a defect sample may show that the control parameters for both elements are within limits, yet a gas hole, characteristic of hydrogen or nitrogen, will appear. In such cases, it is likely that there is a synergistic effect where the elements have

26、combined to form the hole. Here, a full examination of the causes for both gases needs to be undertaken with tighter controls put in place.一般情况下，很难区分出氢气孔和氮气孔，分析缺陷试样有助于显示控制元素的是否在合理的范围之内，然而有时也会出现具有氢气孔和氮气孔特征的，在这种情况下，这些元素对形成氢气孔和氮气孔起共同作用，因此必须采取严密的控制措施来检查缺陷的发生原因。Carbon Monoxide Blowhole一氧化碳气孔The third of

27、the common gas defects is the carbon monoxide blowhole. Figure 3 shows an example of this type of defect, which can normally be seen as a surface blow.CO气孔是灰铸铁中第三种常见的气孔缺陷，图3显示了典型的CO气孔缺陷的例子，这种缺陷经常能够在铸件皮下看见。The carbon monoxide blow can appear as a hole a few millimetres across, as in the illustration

28、here, or in large castings the hole can be large enough to put a fist into. Normally seen in conjunction with slag and clouds of manganese sulphides, it is also possible to see dendrites protruding from the inner surfaces of the hole.像这儿描述的CO气孔直径有几个mm，在的铸件中，大的CO气孔可以塞进一只拳头，其内部常有渣或者硫化锰渣，在其内部也能发现伸进内壁的突

29、出物。Example of surface slag blowhole in grey iron Close-up of defect showing slag cluster灰铸铁中的表面渣孔 聚集的渣的特写Figure 3. Carbon monoxide blowhole 图3 一氧化碳气孔The most common cause of this problem is the failure to totally empty ladles between taps. This results in a lowering of the overall metal temperature

30、and a build up of cold manganese sulphide/oxide rich slags. Eventually, the point is reached where a metal/slag reaction takes place as：造成这种缺陷最普通的原因就是铁水包和出铁口内的铁液没有清理干净，这将导致较低的浇注温度和MnS渣或者氧化物渣在下一包中铁水的聚集。最终这些渣多到一定量就会发生下面的反应：MeO + C = Me = COThe defect may also be attributed to excess manganese and/or s

31、ulphur in the system. These should be balanced according to the equation:这种缺陷归因于铁液中过量的Mn和S，Mn和S的关系应根据下式来计算：%Mn = %S + 0.3Carbon monoxide blowholes can normally be eliminated by ensuring a complete emptying of ladles between taps, operating with clean ladles and preventing slag build up on the refrac

32、tory. Increasing metal temperature can also help.通过完全清理浇包和出铁口，使用干净的浇包和阻止渣在铁液中的累积，增加浇注温度也会对减少CO气孔会有所帮助。Shrinkage收缩缺陷Overview of the position of the shrinkage. The Close-up of the shrinkage showing defect was revealed after machining and was dendrites andmetallic surfacelocated in the centre of the ca

33、sting section with T-shape 缺陷的简图 显示了金属表面和内部枝晶的缩孔特写Figure 4. Example of a hot-spot shrinkage defect 图4：热节收缩缺陷The example shown in Figure 4 is a typical shrinkage defect, typically the surface of the shrinkage hole will show dendrites, but without any graphitic lining as would be seen in a gas related

34、 defect. In the case illustrated, the shrinkage appears at the thermal centre of the casting and the cause was attributed to the sharp radii and to poor metal flow design. Soft sand in the vicinity of the defect may have been a contributory factor in this case.图4 显示的例子是典型的收缩缺陷，缩孔的内壁表面有点型的树枝状枝晶，但是内壁没

35、有石墨膜，石墨膜的出现一般与铸件的气孔缺陷有关。如图描述的收缩缺陷出现在铸件热节的中心，该处铸件较小的圆角和不良的浇注系统设计促使形成了此缺陷，此外热节周围松软的砂型对此缺陷的形成也起了一定的作用。Indeed, the majority of shrinkage defects found in the industry today may be attributed to a soft spot in the moulding sand. Otherwise there are many causes of shrinkage； 实际上，在铸件上发现的大部分的收缩缺陷的原因都归因于松软的砂

36、型，除此之外，还有几种收缩形成的原因：-Thicker sections of a casting that are not properly fed or have inadequate runner/gate designsu:厚壁处的铸件补缩不良或内浇口不够-Low carbon or carbon equivalent irons are more prone to shrinkage due to a lack of low density graphite being precipitated and not providing an "expansion" e

37、ffect to counter the natural solidification shrinkageu C低或者碳当量低，从而造成在凝固过程中没有足够的较低密度的石墨析出来抵消凝固过程中的收缩。-Insufficient clamping or weighting of the mould can lead to liftingu锻铸型没有夹紧或者压铁重量不够造成抬箱-Under-inoculation or over-inoculation both increase the potential for shrinkage, the former due to the lack of

38、precipitated graphite, the later produces too many eutectic cells which can result in porosity between the cells.u 孕育不足和过量孕育也能导致收缩缺陷。前一种情况导致了没有足够的石墨析出，而后一种情况导致了过多的共晶团，太多的共晶团也能导致共晶团之间的缩松。-High phosphorous contents, in excess of 0.1%tend to promote shrinkage, as does excessive pouring temperaturesu 含磷

39、量超过0.1%也能促进缩松缩孔的形成，较高的浇注温度也一样。Inter-cellular Carbides晶间碳化物Figure 5. Example of grain boundary carbides图5：晶界附近的碳化物Today's industry has to cope with decreases in the quality of affordable steel scrap. Often, the trace element content of the steel is higher than has been found previously and there

40、is a resulting increase in the incidence of inter-cellular carbides. These are particularly noted in thicker section castings where the slow solidification time allows for segregation and a build up in the concentration of deleterious elements, such as molybdenum, vanadium, manganese, chromium and t

41、itanium.现在的铸造产业必须面临所使用的废钢质量下降的问题。现在铸造厂所使用的废钢的微量元素含量比以前更高了，这就导致了出现晶间碳化物发生几率的增加。在厚壁铸件中应特别注意这种情况，厚壁处较长的凝固时间使有害元素如Mo、V、Ti、Cr、Mn在晶界上析出和聚集。In some cases, increased or more powerful inoculation will help to disperse the carbide promoting elements and thus the effects of trace elements, avoid the formation

42、of carbides. However, it must be noted that the effects of trace elements，such as those noted above, is cumulative and not individual to the particular elements. Further, some carbide forms, for example Mo and Cr cannot be removed by subsequent heat treatment.在某种情况下，增加孕育剂使用量和使用强效孕育剂可以冲淡碳化物成元素，从而避免碳化

43、物的形成，但是应注意到碳化物元素形成碳化物的效果是累加的。另外对于有些碳化物形成的碳化物，如Cr和Mo，是不能通过随后的热处理来消除这些碳化物的。Avoidance of grain boundary carbides is achieved by careful control of raw materials, particularly steel scrap and by optimising the inoculant addition. Increases in carbon equivalent may also help to disperse the undesirable e

44、lements.通过控制原材料特别是废钢以及优化孕育剂的加入方法可以避免晶间碳化物的产生。增加碳当量也有助于稀释有害的微量元素。Widmanstatten Graphite魏氏体石墨Figure 6 shows a classical example of Widmanstatten graphite. This effect, sometimes referred to as "spiky graphite" is found when levels of the trace elements lead, bismuth or antimony become too hi

45、gh.图6显示了经典的魏氏体石墨组织。这种组织有时也被称作短棒状石墨，当微量元素如Pb、Bi、Sb的含量高时易在铸铁组织中发现。Antimony will promote Widmanstatten graphite in the presence of hydrogen, particularly in heavier section castings, as will bismuth. The usual cause of this defect is the presence of lead, a 0.0005% addition is likely to cause Widmansta

46、tten graphite forms. 特别是铸件的壁厚比较大时，在有氢的存在条件下，Sb促进魏氏体石墨的形成。Bi和Sb的作用一样。产生这种石墨的普通原因就是Pb，当铅的含量为0.0005%时就有可能促进魏氏体石墨的形成。Overview of the graphite structure Close-up of one of the graphite lamellas魏氏体石墨组织图 魏氏体石墨的特写Figure 6. Example of Widmanstatten graphite图6：魏氏体石墨的组织照片The normal sources of lead are free cut

47、ting steels, old painted scrap, vitreous enamelled scrap, terne plate or contamination of the melt with white metals. Melting petrol engines from the days of leaded petrol can also be a source of lead contamination.一般情况下铅来自于废钢种的易切钢，被油污染的废料、带有搪瓷的废钢，镀锌铁板、或被轴承合金污染的废钢，使用废弃的含铅汽油发动机作为回炉料也是铅的一个来源。Widmansta

48、tten graphite has a catastrophic effect on the mechanical properties of the iron, the spikes on the graphite flakes acting as points of weakness to reduce tensile strength values dramatically. The problems with lead tend to arise in induction melted irons as the lead stays within the bath, but is ra

49、rely seen in cupola melted metal as the lead disappears up the stack.魏氏体石墨对灰铸铁的力学性能有着灾难性的影响，石墨上的尖钉起着裂纹的作用，极大的降低了灰铸铁的抗拉强度。用电炉熔炼时铅的含量会上升，而用冲天炉熔炼时则很少出现这种状况，因为铅在加入的批料中铸件消失了。Once lead has appeared in grey iron, there is no real cure except to use a rare earth containing inoculant/preconditioner to try to

50、 scavenge the lead from the iron.一般铅在灰铸铁中的含量超标以后，很少有有效的措施来减少铅的含量，除非使用含有稀土的孕育剂或者是预处理剂来将铅从灰铸铁中清除出来。Steadite斯氏体Steadite in thick section Steadite in thin section厚壁件中的斯氏体 薄壁件中的斯氏体Figure 7. Steadite in grey iron图7：灰铸铁中的磷共晶 Steadite, more commonly known as the phosphide eutectic, is really a precipitation

51、 of iron phosphides. Normally this is not regarded as a defect unless excess phosphorus enters the system and clusters are detected at the grain boundaries.斯氏体，一般叫做磷共晶，实际上是一种磷化铁的析出物。除非铸铁中含有过量的磷共晶或者在晶界上有磷共晶被发现，一般情况下，这不被认为是一种铸造缺陷。Phosphorus has the benefits in iron of increasing fluidity and wear resi

52、stance when present in the right amounts. Less than 0.04% may lead to metal penetration and finning, whilst levels of 0.1%and above can lead to the formation of a network of steadite at grain boundaries with subsequent problems of shrinkage and embrittlement. Some irons are deliberately produced wit

53、h higher phosphorous levels where fluidity is a big issue, radiator castings, stove plates and some electrical casings for example.当铸铁中的磷在合适的范围之内，磷能够提高铁液的流动性和铸件的耐磨性，少于的0.04%的可能导致铸件渗漏，大于0.04的磷会使在晶界上析出连续的斯氏体，这会使铸铁产生收缩缺陷和使铸铁变脆。The cure for excess steadite, apart from reducing the levels of phosphorous,

54、 is to disperse the phosphorous within the casting by improving inoculation or to increase the solidification rate. Care should be taken in the selection of scrap to avoid domestic heating castings and analysis should be made of the pig iron as some brands contain higher levels of phosphorous.除了降低原材

55、料中磷的含量之外，还可以通过加大孕育量和冷却速率来减少铸铁中斯氏体的含量。应该仔细检查废钢和原材料避免家庭供暖用铸件作为炉料，还应该对生铁的磷含量作分析，因为有些品牌的生铁磷含量比较高。Slag渣Example of grey iron slag inclusion cluster Close-up of slag cluster showing various phases灰铸铁中的夹渣 显示了多相的夹渣特写Figure 8. Example of slag inclusions图8 夹渣缺陷Slag inclusions may be found both at the surface o

56、f the casting, as illustrated here, or within the body of the casting. They are recognisable as having no decarburisation associated with them and the slag usually seems to have several different phases within the particle.夹渣也有可能像在这儿描述的一样在铸件表面被发现，也有可能在铸件内部发现夹渣。砂粒周围没有脱碳层并且夹渣是多相共存的，可以通过这种特征来识别夹渣。Slag

57、defects are caused by inadequate slag removal during the melting and pouring phase or by a build up of slag in the pouring ladle or receiver-see also the section on the carbon monoxide blowhole. Slag traps or filters built into the running system often help with the removal of slag, but do not help

58、with the root cause of slag build up and are no substitute for good metal cleaning practise. Slag may also be formed if there is excessive turbulence in the running system or metal is poured from some height. Examination of the runner design or time spent watching the ladle operator's practise is well